Electrical ChargesElectrical Charges

Physics AStatic #1

Learning Targets0I can describe the characteristics (charge,

location, ability to move) of subatomic particles.

0I can calculate the charge of an object using the charge of one electron and the number of electrons that the object is deficient or has in excess.

0I can determine whether an object is positively or negatively charged when given the number of protons and electrons in/on the object.

Static Electricity &the Everyday World

0What are some examples of static electricity that you witness on a regular basis?

0Describe the forces associated with static electricity.

0Why are electrostatic forces important to the everyday world?

0How can an object be charged and what affect does that charge have upon other objects in its vicinity?

Structure of Matter0All material objects are composed of atoms. 0There are different kinds of atoms known as

elements; these elements can combine to form compounds.

0Different compounds have distinctly different properties.

0Material objects are composed of atoms and molecules of these elements and compounds, thus providing different materials with different electrical properties.

Structure of Matter0An atom consists of a nucleus and a vast region of

space outside the nucleus. 0Electrons are present in the region of space outside

the nucleus. 0They are negatively charged and weakly bound to

the atom. 0Electrons are often removed from and added to an

atom by normal everyday occurrences.

Structure of Matter0The nucleus of the atom contains positively

charged protons and neutral neutrons. 0These protons and neutrons are not removable by

usual everyday methods. 0Electrostatic phenomenon can never be explained

by the movement of protons.

Summary of Subatomic Particles

Summary of Subatomic Particles

Electron Affinity0The presence of different atoms in objects provides

different objects with different electrical properties.

0Electron Affinity: the relative amount of attraction that a material has for electrons 0If atoms of a material have a high electron affinity,

then that material will have a relatively high attraction to electrons.

Neutral vs. Charged Objects0A proton and an electron have an equal amount but an

opposite type of charge. 0If an atom contains equal numbers of protons and

electrons, the atom is described as being electrically neutral.

0If an atom has an unequal number of protons and electrons, then the atom is electrically charged.0Any particle that contains less electrons than protons is

said to be positively charged.0Any particle that contains more electrons than protons is

said to be negatively charged.

Neutral vs. Charged Objects

Positively Charged

Negatively Charged Uncharged

Charge as a Quantity0The charge of an object is a measurable quantity.0The charge possessed by an object is expressed using the

unit known as the Coulomb (C). 0One Coulomb of charge is an abnormally large quantity of

charge, the units of microCoulombs (µC) or nanoCoulombs (nC) are more commonly used as the unit of measurement of charge.

Charge as a Quantity0The charge on a single electron is -1.6 x 10 -19 Coulomb.

0What is the charge on a single proton?

0The quantity of charge on an object reflects the amount of imbalance between electrons and protons on that object.

Charge as a Quantity0 In conclusion, an electrically neutral object is an object that

has a balance of protons and electrons. 0 In contrast, a charged object has an imbalance of protons

and electrons.

€

# protons−#electrons * 1.6*10−19( )

____ are the charged parts of an atom.

a. Only electronsb. Only protonsc. Neutrons onlyd. Electrons and neutronse. Electrons and protonsf. Protons and neutrons

TRUE or FALSE: An object that is positively charged contains all

protons and no electrons.

TRUE or FALSE: An object that is negatively charged could contain

only electrons with no accompanying protons.

TRUE or FALSE: An object that is electrically neutral contains only

neutrons.

Identify the following particles as being charged or uncharged. If charged, indicate whether they are charged

positively or negatively.

Identify the following particles as being charged or uncharged. If charged, indicate whether they are charged

positively or negatively.

Consider the graphic below of a neutral oxygen atom.

Explain what must happen in order for the oxygen

atom to become negatively charged.

Consider the graphic below of a neutral oxygen atom.

Explain what must happen in order for the oxygen

atom to become positively charged.

Determine the quantity and type of charge on an object that has 3.62 x 1012

more protons than electrons.

Determine the quantity and type of charge on an object that has 4.51 x 105

more electrons than protons.

After some rather exhausting counting, a physics teacher determines that a very small sample of an object contains 8.25749 x 1017

protons and 5.26 x 1014 electrons; the charge on this object is ____ Coulombs.

After some rather exhausting counting, a physics teacher determines that a very small

sample of an object contains 3.12 x 1014 protons and 4.5488 x 1016

electrons; the charge on this object is ____ C.

The amount of charge carried by a lightning bolt is estimated at 10

Coulombs. What quantity of excess electrons is carried by the lightning bolt?

Learning Targets0I can determine whether the electric force

between charged objects is attractive or repulsive based on the types of charges.

0I can compare the electric interactions between charged objects in order to determine the charge of each object.

The Electric Force & Newton's 3rd Law

0Being a force, the same laws and principles that describe any force describe the electrical force.

0According to Newton's third law (the action-reaction law), a force is simply a mutual interaction between two objects that results in an equal and opposite push or pull upon those objects.

The Electric Force & Newton's 3rd Law0Object A exerts a rightward push upon Object B.

Object B exerts a leftward push upon Object A. 0These two pushing forces have

equal magnitudes and are exerted in opposite directions of each other.

0Why are these called repulsive forces?

0Why do they objects repel in this situation?

The Electric Force & Newton's 3rd Law0Object C exerts a leftward pull upon object D.

Object D exerts a rightward pull upon Object C. 0Each object does its own pulling of

the other. 0These two forces have equal

magnitudes and are exerted in opposite directions of each other.

0However in this instance, the direction of the force on Object D is towards Object C and the direction of the force on Object C is towards object D. Because of the towards each other nature of the mutual interaction, the force is described as being attractive.

Interaction Between Charged and Neutral Objects

0Any charged object - whether positively charged or negatively charged - will have an attractive interaction with a neutral object. 0Positively charged objects and neutral objects attract each other.0Negatively charged objects and neutral objects attract each other.

Electrical forces ____.

a. can cause objects to only attract each otherb. can cause objects to only repel each otherc. can cause objects to attract or repel each otherd. have no effect on objects

The following charge interactions between balloons A, B & C are observed. It is known that balloon B is charged negatively. What

can you conclusively confirm about the charge on balloon A & C.

Upon entering the room, you observe two balloons suspended from the ceiling. You

notice that instead of hanging straight down vertically, the balloons seem to be repelling

each other. You can conclusively say …a. both balloons have a negative charge.b. both balloons have a positive charge.c. one balloon is charge positively and the other negatively.d. both balloons are charged with the same type of charge.

A student is investigating the charge on several objects and makes the following findings.

He knows that object A is negatively charged and object B is electrically neutral. What can he definitively conclude about the charge on objects C, D, E, and F? Explain.

Two objects are charged as shown. Object X will ___ object Y.

a. attractb. repelc. not affect

Two objects are shown. One is neutral and the other is negative.

Object X will ____ object Y.

a. attractb. repelc. not affect

Balloons X , Y and Z are suspended from strings as shown. Negatively charged

balloon X attracts balloon Y and balloon Y attracts balloon Z. Balloon Z ____.

a. may be positively chargedb. may be negatively chargedc. may be neutrald. must be positively chargede. must be negatively chargedf. must be neutral

Learning Targets0I can describe the properties of insulators and

conductors.

0I can explain why an attractive force results from bringing a charged object near a neutral object.

0I can draw the redistribution of electric charges on a neutral object when a charged object is brought near.

Conductors0The behavior of an object that has been charged is

dependent upon whether the object is made of a conductive or a nonconductive material.

0Conductors are materials that permit electrons to flow freely from particle to particle.0An object made of a conducting material will permit charge

to be transferred across the entire surface of the object.0Conductors allow for charge transfer through the free

movement of electrons.

Insulators0Insulators are materials that impede the free flow of

electrons from atom to atom and molecule to molecule.0 If charge is transferred to an insulator at a given location,

the excess charge will remain at the initial location of charging.

0The particles of the insulator do not permit the free flow of electrons.

Insulators0While insulators are not useful for transferring

charge, they do serve a critical role in electrostatic experiments. 0What are some important uses of insulators?

Examples of Conductors & Insulators

One of these isolated charged spheres is copper and the other is rubber. The diagram below depicts the distribution of excess negative

charge over the surface of two spheres. Label which is which and support your answer.

Which of the following materials are likely to exhibit more conductive

properties than insulating properties?

a. rubberb. aluminumc. silverd. plastice. wet skin

A conductor differs from an insulator in that a conductor ________.

a. has an excess of protonsb. has an excess of electronsc. can become charged and an insulator cannotd. has faster moving moleculese. does not have any neutrons to get in the way of electron flowf. none of these

Suppose that a conducting sphere is charged positively by some method. The charge is initially

deposited on the left side of the sphere. Yet because the object is conductive, the charge

spreads uniformly throughout the surface of the sphere. The uniform distribution of charge is

explained by the fact that ____.a. the charged atoms at the location of charge move throughout the surface of the sphereb. the excess protons move from the location of charge to the rest of the spherec. excess electrons from the rest of the sphere are attracted towards the excess protons

When an oil tanker car has arrived at its destination, it prepares to empty its fuel into a reservoir or tank. Part of the preparation involves connecting the body of the tanker

car with a metal wire to the ground. Suggest a reason for why is this done.

Polarization0In conducting objects, they are so loosely bound

that they may be induced into moving from one portion of the object to another portion of the object.

Polarization of Conductors0Polarization is the process of separating opposite

charges within an object. 0The positive charge becomes separated from the

negative charge. 0By inducing the movement of electrons within an object,

one side of the object is left with an excess of positive charge and the other side of the object is left with an excess of negative charge.

0Charge becomes separated into opposites.0The polarization process always involves the use of a

charged object to induce electron movement or electron rearrangement.

How Can an Insulator be Polarized?

Examples of Polarization

Polarization is Not Charging0When an object becomes polarized, there is

simply a redistribution of the centers of positive and negative charges within the object. 0There are still equal numbers of positive

charges and negative charges within the object. 0When neutral objects become polarized, they

are still neutral objects.

A rubber balloon possesses a positive charge. If brought near and touched to the door of a

wooden cabinet, it sticks to the door. This does not occur with an uncharged balloon.

These two observations can lead one to conclude that the wall is _____.

a. electrically neutralb. negatively chargedc. a conductord. lacking electrons

Which of the diagrams below best represents the charge distribution on a metal sphere when a positively charged plastic tube is

placed nearby?

The distribution of electric charge in a H2O molecule is nonuniform. The more electronegative oxygen atom attracts electrons from the hydrogen atom. Thus, the

oxygen atoms acquire a partial negative charge and the hydrogen atoms acquire a partial positive charge. The

water molecule is "polarized." Which diagram(s) below correctly portray(s) a pair of H2O molecules? Explain.

True or False: When an object becomes polarized, it

acquires a charge and becomes a charged object.

Charged rubber rods are placed near a neutral conducting sphere, causing a redistribution of charge on the spheres. Which of the diagrams below depict the proper distribution of charge

on the spheres? List all that apply.

In the above situation, the conducting sphere is ____. List all that apply.

a. chargedb. uncharged (neutral)c. polarized